At present, there are two ways, i.e. in series and in parallel for accessing a memory data. Taking the former one for example, as shown in FIG. 1, the relevant block diagram includes an input register 11, a decoding memory unit 12 for storing therein data to be accessed, and an output register 13 in the same integrated circuit (IC) package having AIN, DOUT, CLK and CS pins. Also referring to FIG. 2, the accessing operation in series is described as follows:
When the CS pin is LOW, IC 10 is enabled so that CLK pin receives a clock signal and pin AIN receives an address signal. If an address in decoding memory unit 12 has 14 bits, pin AIN will receive a bit each time in series 14 address signals A0-A13 which are outputted by input register 11 after having sequentially received address signals A0-A13. After address signals A0-A13 have been received and decoded by decoding memory unit 12, decoding memory unit 12 outputs data D0-D7 corresponding to address signals A0-A13 to output register 13 outputting in turn a bit at one time data D0-D7 in series from pin DOUT. The advantage of this accessing way resides in that the interface circuit for accessing decoding memory unit 12 only requires an address pin and a data output pin. Accordingly, when the memory capacity of decoding memory unit 12 is desired to be expanded, what is needed is to increase the bit numbers of the input addresses or to externally connect to decoding memory unit 12 a plurality of identical IC packages 10 without the necessity of changing the pin number of the IC package 10.
When the required memory capacity exceeds the maximum capacity of a single memory, an external decoder in addition to the connection of plural identical IC packages 10 is needed for distinguishing among identical memories, as shown in FIG. 3 which shows an expanded memory 30 which includes pins AN, DOUT, CLK and CS and 4 memories 31-34 respectively including pins AIN1-AIN4, DOUT1-DOUT4, CLK1-CLK4 and CS1-CS4. It can be seen that a 2-to-4 decoder 35 needs two extra signal wires EXT0 and EXT1. If an even larger capacity of memory 30 is desired, additional decoders and signal wires are conceivably to be required which will inevitably complicate the relevant circuit design.
To access a memory data in parallel is exemplarily shown in FIG. 4 showing a decoding memory unit 4 which receives and then decodes at the same time 14 address signals A0-A13, then outputs at the same time data corresponding to address signals A0-A13, and thus requires 14 address pins PA0-PA13 and 8 data output pins PD0-PD7. It can be found that decoding memory unit 4 also includes a chip selection pin CS and an output enabling pin OE. FIG. 5 shows timing signals of pins shown in FIG. 4. The advantage of parallelly accessing the memory data is the fast accessing speed since every bit address and data are respectively received and outputted from corresponding pins so that a full data can be accessed at a time. Nevertheless, it has disadvantages as follows:
1) Every chip has a great many of pins to result in a relatively high packaging cost. PA1 2) The controller for controlling decoding memory unit 4 must be provided with equal pins for controlling address and data pins of decoding memory unit 4 so that too many controlling pins of the controller are so occupied. PA1 3) If decoding memory unit 4 is to be expanded, its pin number will be significantly increased so that the layout of the peripheral control system needs be newly designed as shown in FIG. 6 showing an expanded parallel memory device 60 which includes pins A0-A5, WR and CS and 4 series-connected memories 61-64 respectively having pins A01-A04, A11-A14, A21-A24, A31-A34, A41-A44, A51-A54, WR1-WR4 and CS1-CS4. It also can be found that there additionally are a 2-to-4 decoder 65 and two signal wires A6 and A7. If an even larger capacity of memory device 60 is desired, additional decoders and signal wires are conceivably to be required which will inevitably complicate the relevant circuit design.
It is therefore attempted by the Applicant to deal with the problems encountered by the prior art.